1. Field of the Invention
The present invention relates to a fuel injection control device for engines with a common-rail type fuel injection system which stores in a common rail a fuel pressurized to a predetermined pressure by a fuel pump and injects the stored fuel from injectors into combustion chambers.
2. Description of the Prior Art
As for the fuel injection control in engines, a common-rail type fuel injection system has been known which provides a high injection pressure and performs optimum control on injection characteristics, such as fuel injection timing and the amount of fuel injected, according to the operating condition of the engine. The common-rail type fuel injection system is a fuel injection system that stores in the common rail a fuel pressurized to a predetermined pressure by a pump and then injects the stored fuel from injectors into corresponding combustion chambers. To ensure that the pressurized fuel will be injected from each injector under optimum injection conditions according to the engine operating conditions, a controller controls the fuel pressure in the common rail and the operation of control valves for the injectors according to the operating conditions of the engine.
The conventional common-rail type fuel injection system will be described by referring to FIG. 11. The fuel is supplied to individual injectors 1 from a common rail 2 through branch pipes 3 that form a part of the fuel passage. The fuel, which was pumped by a feed pump 6 from a fuel tank 4 through a filter 5 and pressurized to a predetermined pressure, is delivered to a fuel pump 8 through a fuel pipe 7. The fuel pump 8 may, for example, be a so-called plunger type fuel supply pump driven by the engine which raises the fuel pressure to a high pressure determined by the operating condition of the engine and delivers the pressurized fuel through a fuel pipe 9 to the common rail 2. The fuel is then stored temporarily in the common rail 2 at the elevated pressure, from which it is supplied to individual injectors 1. Normally there are provided two or more injectors 1 corresponding in number to cylinders in the engine (or according to the type of engine). These injectors 1 are controlled by a controller 12 to inject fuel supplied from the common rail 2 into the corresponding combustion chambers in optimum amounts and at optimum timings. Because the pressure at which the fuel is injected from the injectors 1 is equal to the pressure of the fuel stored in the common rail 2, the injection pressure is controlled by controlling the fuel pressure in the common rail 2.
The fuel flowing from the feed pump 6 into the fuel pump 8 is controlled by a flow control valve 10. Of the fuel supplied from the branch pipes 3 to the injectors 1, the fuel that was not used for injection into the combustion chambers is returned to the fuel tank 4 through a return pipe 11. The controller 12 as an electronic control unit (ECU) is supplied with information on the engine operating condition from various sensors, which include: engine cylinder determination and crank angle sensors for detecting an engine revolution speed Ne, determining the cylinders into which the fuel needs to be injected and calculating the injection timing; an accelerator opening sensor for detecting the accelerator control input Acc such as an accelerator depression; a water temperature sensor for detecting the cooling water temperature; and an intake pipe inner pressure sensor for detecting the inner pressure of the intake pipe. The controller 12, based on these signals, controls the fuel injection characteristics of the injectors 1, i.e., the fuel injection timing and the amount of fuel to be injected (injection pressure and injection period) so that the operation characteristics such as engine output, exhaust gas and mileage will become optimum for the current engine operating condition. The common rail 2 is provided with a pressure sensor 13 which detects the fuel pressure in the common rail 2 and sends the detection signal to the controller 12. Once the fuel is injected from the injectors 1, the fuel in the common rail 2 is consumed reducing the pressure in the common rail 2. The controller 12 controls the flow control valve 10 to regulate the amount of fuel delivered by the fuel pump 8 to the common rail 2 so as to maintain the fuel pressure in the common rail 2 at a preset pressure.
An example of the conventional fuel injection control device for internal combustion engines is disclosed in Japanese Patent Laid-Open No. 50649/1988. This fuel injection control device for internal combustion engines comprises a common rail of a certain volume, a fuel supply pump to deliver fuel to the common rail through the fuel supply passage, fuel injection valves to inject fuel supplied to the common rail into the combustion chambers, a flow regulating valve to regulate the amount of fuel flowing from the fuel tank to the fuel supply pump, a pressure detection means to detect a common rail pressure, an operating condition detection means to detect the operating condition of the internal combustion engine, a pressure setting means to set a target pressure of the common rail based on the result of detection by the operating condition detection means, and a pressure control means to control the flow regulating valve according to the result of detection by the pressure detection means and also control the common rail pressure to the target pressure.
With the fuel injection control device for internal combustion engines disclosed in the above official gazette, a flow control valve for controlling the fuel flow from the fuel tank is installed at the suction side of the fuel supply pump that supplies a high-pressure fuel to the fuel injection valves through the fuel supply passage including the common rail. The flow control valve is controlled by the pressure control means to eliminate the deviation between the target fuel pressure in the fuel supply passage, which is set according to the result of detection by the engine operating condition detection means, and the actual fuel pressure in the fuel supply passage. The control of fuel flow performed by the flow control valve is done by changing the cross section of the fuel passage or by controlling the duty ratio to change the valve opening time. When the actual fuel pressure in the fuel supply passage is detected to be higher than the target fuel pressure by more than a predetermined threshold range, the flow control valve performs control to reduce the fuel flow to the fuel supply pump. This in turn reduces the fuel flow delivered by the fuel supply pump to the common rail, resulting in an immediate reduction in the fuel pressure in the pressure accumulation chamber.
The fuel supply pump used in the above fuel injection control device has a stationary shaft fixedly supported in a pump casing, a rotor turning around the stationary shaft, and a ring rotatably supported on the pump casing through a bearing. The rotor has many radial pistons arranged radially therein and shoes inserted between each radial piston and the ring that rotate with the radial pistons. The stationary shaft is formed with a suction port communicating with the flow regulating valve and a delivery port communicating with the common rail. As the rotor turns, the cylinder chambers in which each radial piston reciprocates are brought into communication with the suction port and the delivery port alternately. The alternate communication is synchronized with radially outward or inward displacement of the radial pistons causing the fuel to be discharged from the delivery port.
How the common rail pressure changes is shown at the common rail pressure P in the graph of FIG. 1. The graph of FIG. 1 represents a four-cylinder engine with a one-to-one correspondence between each pump chamber and the injector of each cylinder into which the fuel is to be injected. The cylinder determination sensor generates a cylinder determination signal (REF signal) at a position 120xc2x0 crank angle before the top dead center of No. 1 piston (firstly-operated piston). A before-top-dead-center sensor generates a before-top-dead-center (BTDC) signal at a position 60xc2x0 crank angle before the top dead center for each piston.
Immediately before the pistons reach their top dead centers one after another, a drive pulse to drive an on-off valve such as a needle valve that directly controls the fuel injection from the injector corresponding to the cylinder of interest is generated. A drive pulse Ip1 fed to No. 1 injector (firstly-operated injector) corresponding to No. 1 cylinder (firstly-operated cylinder) activates the firstly-operated injector. When the firstly-operated injector injects fuel, the common rail pressure decreases as shown at Pd1. When the fuel injection from the firstly-operated injector is finished, however, No. 2 piston (secondly-operated piston) of the fuel pump that has already entered the delivery process delivers the fuel from No. 2 pump chamber (secondly-operated pump chamber) and thus the common rail pressure recovers as shown at Pf(1). Next, as a drive pulse Ip2 is sent to No. 2 injector (secondly-operated injector) to inject fuel, the common rail pressure falls again as shown at Pd2. But because the fuel is delivered from No. 3 pump chamber (thirdly-operated pump chamber), the common rail pressure recovers again as shown at Pf(2). In this way, the common rail pressure repeats the process of falling as a result of fuel injection performed successively by the injectors (as shown at Pd1, Pd2, Pd3, Pd4) and then recovering by the fuel delivery from the pump chambers of the fuel pump (as shown at Pf(1), Pf(2), Pf(3), Pf(4)).
In the common-rail type fuel injection device which controls the fuel flow from the pump by means of a pump inlet flow control valve and which uses a plurality of pump chambers operated successively at each fuel injection from the injectors, pressure variations are caused in synchronism with the pump rotation period by variations specific to the individual pump chambers such as dimensional variations and operation timing variations. The dimensional variations include those of the pistons and cylinders, of the slits and other portions of the flow control valves, and of the fuel passages and check valves corresponding to the individual pump chambers of the fuel pump. That is, as shown at the common rail pressure P in the graph of FIG. 1, the common rail pressure that is recovered by the fuel delivered by the successively activating pump chambers is not constant on each recovery but differs from one recovery to another, varying in synchronism with the pump rotation period. The similar phenomenon occurs also when the flow control valve is installed at the delivery side of the fuel pump. The fuel injection control device disclosed in the above official gazette, however, does not consider the variations among the cylinders of the fuel supply pump and the resulting common rail pressure variations.
When there are variations in the amount of fuel delivered, the pressure at which the fuel starts to be injected differs among the cylinders from the target injection pressure even when the engine is running in a steady state. If the common rail pressure, which is recovered by the fuel delivered from the fuel pump having a plurality of pump chambers, varies from one recovery to another, the engine output is likely to vary especially when engine revolution speed is low, causing engine vibrations and noise, leading to increased exhaust emissions. This tendency is significant particularly when the engine is idling. Hence, to reduce variations in the amount of fuel injected from the injectors and stabilize the rotation of the engine output shaft during the idling to reduce engine vibrations and noise and prevent deterioration of exhaust emissions, there are demands for equalizing the amounts of fuel delivered successively from individual pump chambers of the fuel pump to reduce variations in the recovery pressure of the common rail after each fuel injection.
The object of this invention is to solve the above problems and to provide a fuel injection control device for engines which-based on that fact that in a common-rail type fuel injection system variations of the common rail pressure recovered following the pressure drop caused by fuel injection have a correlation with variations of the amount of fuel delivered by each piston-corrects the operation of the flow control valve at a timing that the corresponding piston is in a suction stroke according to the deviation of the recovered common rail pressure so as to equalize a common rail pressure.
This invention relates to a fuel injection control device for engines which comprises: a common rail to store fuel delivered by a fuel pump; injectors to inject fuel supplied from the common rail into combustion chambers; a pressure sensor to detect a pressure of the common rail; and a controller to control the amount of fuel delivered from the fuel pump according to the pressure of the common rail detected by the pressure sensor; wherein the fuel pump has pump chambers that are successively activated to deliver fuel each time the injectors have injected fuel; wherein, based on the difference between the common rail recovery pressures provided by the fuel delivered from two successively operated pump chambers of the fuel pump, the controller controls the amount of fuel delivered by the second-operated of the two pump chambers in order to minimize variations of the common rail pressure.
Because this fuel injection control device is constructed as described above, when the common rail pressures that are recovered by the fuel delivered from the successively operated two of the pump chambers of the fuel pump differ from each other, this pressure difference has a correlation with the amounts of fuel delivered from the two successively operated pump chambers. Hence, based on the pressure difference, the amounts of fuel to be supplied to the pump chambers are controlled to equalize the amounts of fuel delivered from these pump chambers, thus reducing the variations of the common rail pressure. This in turn stabilizes the amounts of fuel injected from the injectors that receive fuel from the common rail, contributing in particular to stabilization of the engine output shaft rotation during idling, reducing the engine vibrations and noise and preventing deterioration of exhaust emissions.
The control on the amount of fuel delivered by the fuel pump is performed by controlling a flow control valve provided on the inflow side of the fuel pump to control the amount of fuel supplied to the pump chambers. Changing the amount of fuel supplied to each pump chamber of the fuel pump as by controlling the opening of the flow control valve changes the amount of fuel delivered from the corresponding pump chamber.
An operation state detection means for detecting an operating state of the engine is provided, and the controller determines a target pressure of the common rail based on the operating state of the engine detected by the operation state detection means and controls the flow control valve to match the pressure of the common rail with the target pressure. Generally, the common rail target pressure is determined according to the operating state of the engine, i.e., whether the engine is in a non-steady state such as acceleration or deceleration, or to the magnitude of load, and the flow control valve is controlled so that the common rail pressure will match the target pressure.
Further, the control on the amount of fuel delivered from the fuel pump based on the difference between the recovered common rail pressures is performed when the engine operation state detected by the operation state detection means indicates idling and the target pressure of the common rail is equal to or less than a predetermined threshold value. As described earlier, the effects the common rail pressure variations have on the engine revolution speed variations are greatest during the idling. Hence, by performing the common rail pressure equalization control based on the difference between the successive common rail recovery pressures at least when the engine is idling and is in a stable state where the common rail target pressure does not change in excess of the predetermined threshold range, the vibrations, noise and exhaust emissions characteristics can effectively be improved.